The problems linked to the perspiration of feet inside shoes are known.
It is widely known that most of the perspiration of the foot is generated at the interface between the sole of the foot and the sole of the shoe, and the sweat that forms there, being unable to evaporate, condenses on the plantar insert on which the foot rests; only a minimal part of the sweat evaporates through the upper.
This phenomenon is particularly felt in shoes with a rubber sole; in this case, vapor permeability through the sole is completely prevented.
Solutions to the problem are provided by vapor-permeable and waterproof soles such as the one disclosed in U.S. Pat. No. 5,044,096 and EP-0382904 by the same Applicant, which consists in dividing the rubber sole into two layers with through holes and in interposing a membrane which is impermeable to water and permeable to vapor and is joined peripherally and hermetically to the two layers, so as to not allow water infiltrations.
Subsequent improvements have interposed the vapor-permeable membrane between vapor-permeable or perforated layers of protective material and fillers.
Such perforated soles provided with waterproof and vapor-permeable membranes certainly have constituted remarkable innovations with respect to what was available earlier.
In this regard, it is known to provide a waterproof and vapor-permeable shoe comprising a waterproof and vapor-permeable sole which is injected directly onto a waterproof and vapor-permeable upper fitted on a last for direct injection mold.
According to this manufacturing method, a first lower tread element provided with holes is injected into a first mold.
The lower perforated tread element, a protective element arranged above the lower tread, at the holes, and a waterproof and vapor-permeable membrane above the protective element, are then inserted in a second mold.
Above the membrane there is a vapor-permeable filler, which has a smaller extension than the membrane so as to leave a peripheral surface of said membrane exposed.
This second mold is closed so that the insole of the assembled upper compresses sufficiently the three elements against the lower tread element.
By injecting the second part of the tread, a peripheral seal is formed and the structure of the shoe becomes monolithic.
In practice, the membrane is thus joined hermetically to the midsole and to the tread.
Currently, the need is felt to provide treads which have articulated peripheral elements, such as for example wings which rise externally on the midsole so as to form grip elements arranged laterally to the sole, which besides having retention functions have a particular visual effect; for example, the tread can have a different color with respect to the midsole.
With this type of tread, it is extremely difficult to overmold the midsole onto the tread.
During injection molding of the midsole onto the tread, the articulated peripheral elements in fact tend to rise, making it in practice impossible to obtain correct overmolding.